The overall objective of the proposed research is to study the normal development of the cat retinogeniculate pathway in terms of 1) the prenatal development of the lateral geniculate nucleus, including the time course of geniculate cell birth, the migration of cells destined to form the lateral geniculate nucleus and the formation and subsequent lamination of the nucleus, and 2) the relationship between geniculate cell birthdate, soma size and location and dendritic and axonal morphology. The relationship between geniculate cell birthdate and functional class will be studied indirectly at first. Then, at a somewhat later time, after all indirect comparisons have been made, this latter relationship will be studied directly using a combination of extracellular and intracellular recording techniques, intracellular staining techniques and autoradiographic procedures. Briefly, the following approaches will be used. Kitten fetuses will be exposed to single 'pulse' injections of H3-thymidine at different times during embryonal development. The available thymidine is taken up by the cells that are dividing in each kitten fetus, thus 'tagging' sub-populations of geniculate cells with similar birthdates. By then taking kitten fetuses at various times prior to birth, the prenatal development of each sub-population of geniculate cells can be studied using standard autoradiographic techniques. In radioactively labeled animals allowed to mature normally, the morphology of geniculate cells with known birthdates will be studied using both horseradish peroxidase and Golgi techniques, coupled with the autoradiographic procedures.